1. Field of the Invention
The present invention relates to a heat sensing type acceleration sensor.
2. Description of Related Art
Recently, MEMS (Micro Electro Mechanical Systems) have received increasing attention. The MEMS are microscopic electronic mechanical system parts/elements which are produced by means of semiconductor microfabrication techniques. As a typical MEMS, an acceleration sensor is known for detecting acceleration of an object.
For example, a heat sensing type acceleration sensor includes a substrate having a recess on the surface thereof, four thermocouples installed on the recess, and a heater disposed at the center of the four thermocouples. Among the four thermocouples, two the thermocouples are disposed along the X axis at mutually opposite sides at equal intervals with respect to the heater, and the other two the thermocouples are disposed along the Y axis orthogonal to the X axis at mutually opposite sides at equal intervals with respect to the heater.
When the heater is energized, the surrounding air is heated by the heat from the heater, and temperature gradients symmetrical with respect to the X axis direction and the Y axis direction are generated. The pairs of the thermocouples disposed on the X axis and the Y axis, respectively, are disposed at equal intervals from the heater, so that when the acceleration sensor stands stationary, a temperature difference detected by each pair of the thermocouples is zero. On the other hand, when acceleration in the X axis direction is applied to the acceleration sensor, the air temperature distribution shifts to the X axis direction, and the temperatures detected by the pair of the thermocouples disposed on the X axis become different from each other. When acceleration in the Y axis direction is applied to the acceleration sensor, the air temperature distribution shifts to the Y axis direction, and the temperatures detected by the pair of the thermocouples disposed on the Y axis become different from each other. Therefore, based on the temperature differences detected by the respective pairs of the thermocouples, a direction and magnitude of acceleration applied to the acceleration sensor can be detected.
However, in the above-described heat sensing type acceleration sensor, it is necessary to form a recess on the surface of the substrate and to install a heater and four thermocouples on the recess, resulting in complicated production process and high cost.